Brackish Aquarium Basics

Looking for something different in the aquarium hobby? Then a brackish water aquarium may just be the endeavor for you. They are easy to maintain since the fish from brackish waters are designed to withstand frequent salinity and water parameter changes unlike both fresh and saltwater fish. The following is a basic overview of how to set-up and maintain a tropical brackish aquarium.


The first step before any well planned aquarium is research. Take the time to think about what kinds of fish you would like to keep. By pre-planning you are better assured that the fish you choose will be appropriate tank mates.

Aquarium Size

Almost any size aquarium is suitable for brackish fish. However, the smaller the aquarium, the smaller and fewer the fish you can put in it. Due to the adult size of many brackish fish, bigger is better. A larger ecosystem can better handle the daily fluctuations in water quality than a small ecosystem, absorbing more toxins and reducing stress on the fish. Before buying your aquarium, take into account the adult size of the fish you are going to purchase and this general rule: one inch of fish body (not including fins) per two gallons of water in the brackish aquarium.

Setting Up Your Aquarium

You will need good filtration, either a hang on power filter, a canister filter, or a wet-dry system (for larger or heavily stocked tanks). Check with one of our staff members, as these types vary with the size of aquarium and fish desired.

Substrate or gravel for the brackish aquarium should be sand. This can be any saltwater aragonite sand or even children's play sand.

A heater is required for brackish set-ups; set your temperature between 76 and 80 degrees.

Lighting is another consideration, but how much you will need varies. If you are only keeping fish (no live plants) a simple fluorescent bulb fixture will suffice. If you find you are having an algae problem reduce the hours the lighting is on.

Be sure to have test kits on hand to monitor your water chemistry. Test the water in your new aquarium at least twice a week for pH, Ammonia, Nitrite, and Nitrate. Carbonate Hardness are also good tests to have available. The pH levels in brackish aquariums vary depending on the type of habitat, falling between 7.5 and 8.5.

Brackish aquariums require marine salt mixes, and not freshwater salt. Mix your salt directly in the aquarium when first setting up. Check the salinity with a hydrometer. Salinity (or specific gravity) requirements vary with the fish you choose. Many brackish estuary fish will require slow increases in salinity as they grow to adults, eventually reaching full marine salinity. Most brackish fish, like puffers, datnoids, mollies and gobies, however, do well on 2 tablespoons of salt per gallon of water.

Cycling Your Aquarium & Adding Fish

Before adding your favorite fish, your tank must "cycle" or become biologically stable. Cycling is the process where a nitrifying bacteria colonizes in your filter and gravel. This bacteria's job is to detoxify the wastes created by your fish. You will notice that within the first few weeks by testing your water, ammonia and nitrite levels will rise in the tank and slowly decrease. Also during this time you may see the water in the aquarium start to cloud or look grey. Do not worry, this is natural, the cloudiness will pass quickly on its own, or you can add a bacteria supplement such as Stress Zyme or Cycle to help lower ammonia levels and aid in the cycle.

Fish can be added about three days after setting up your aquarium. This time allows all the salt to mix, and temperature and pH stabilize. To get started, you need to begin with starter fish. The cycling process is very stressful for most fish so we recommend hearty starters. These are usually black mollies for the brackish aquarium.

While your aquarium is cycling do not change any water, clean out your filter media or add more fish. Your tank will be completely cycled when ammonia and nitrite both test at zero and nitrate tests low. This can take anywhere from 3 to 8 weeks. The key here is to be patient.

New Fish and Maintenance

When your aquarium is cycled, add new fish gradually. Adding too many fish at once can disrupt your cycle and increase the possibility of fish illness. Be sure to follow recommended acclimating procedures to ensure a happy addition.

Once cycled, basic aquarium maintenance includes feeding, cleaning, and water changes. When your purchase your new fish, find out what food is best and how often they should be fed. Brackish foods are available in dried and frozen varieties and each type of fish has different needs. Cleaning includes scraping aquarium walls to keep them free of algae and stirring the sand on a regular basis. Water changes are crucial to keeping your tank healthy. Never change more than 25% of the aquarium water at one time. Changing too much can do much more harm than good. Normal water changes should be done approximately every 14 to 18 days. This keeps nitrate levels low and ensures healthy fish. Always pre-mix your brackish water in a container before adding it back into the aquarium and make sure the temperature and specific gravity is equal to that already in the aquarium.

With this basic information you are well on your way to keeping a brackish aquarium. If at any time you have any questions or need help selecting fish or supplies for your aquarium, feel free to contact the fish room at 717-299-5691 ext. 1213 or You can also find informative articles on That Fish Blog at or post your questions on our Facebook page. We at That Fish Place - That Pet Place want to keep you and your fish happy for years to come!

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